This invention relates to internal combustion engines having at least one intake and exhaust valves arranged to scavenge exhaust gases from the combustion chamber.
In conventional external-ignition two-stroke internal combustion engines, and sometimes in four-stroke engines as well, fresh gas, i.e., air in the case of direct fuel injection or a fuel-air mixture in the case of intake injection or carburetor engines, may be supplied during an overlap of the open phases of the inlet and outlet valve to force the exhaust formed in the combustion chamber during the previous cycle through the open outlet valve into an exhaust line. One disadvantage of this arrangement is that, with declining engine load, the volume of fresh gas delivered to the combustion chamber is reduced so that, as the engine load decreases, the exhaust content of the mixture in the combustion chamber increases, adversely affecting the rate of combustion and the completeness of combustion of the mixture in the combustion chamber.